The present application relates to turbomachines, and more particularly, to turbomachines for use in aircraft environmental control systems.
Aircraft environmental control systems incorporate turbomachines, commonly referred to as an air cycle machines, to help facilitate cooling and dehumidifying air for supply to a cabin of an aircraft. Air cycle machines can comprise two or more wheels, which comprise at least one compressor and at least one turbine, disposed axially along the same shaft. On aircraft powered by gas turbine engines, the air to be conditioned in the air cycle machine is generally either compressed air bled from one or more of the compressor stages of the gas turbine engine, or air diverted from another location on the aircraft. With either system, the air is passed through the compressor(s) of the air cycle machine where it is further compressed, and then passed through a heat exchanger to cool the compressed air sufficiently to condense moisture therefrom. The dehumidified air continues through the environmental control system back to the turbine(s) of the air cycle machine. In the turbine(s), the air is expanded to both extract energy from the compressed air so as to drive the shaft (and the compressor(s) coupled thereto) and cool the air for use in the cabin as conditioned cooling air.
To meet required specifications for providing fresh air and maintain pressurization to the cabin during flight, environmental control systems on larger aircraft employ two separate (dual) air conditioning packs. Unfortunately, operating dual air conditioning packs may not be necessary or efficient in some circumstances such as when the plane is on the tarmac. In this instance and others, operating only a single air conditioning pack could accomplish the conditioning of air for the cabin.